It has been ascertained that 5-HT.sub.3 receptors, which are of one class of the subtypes of the serotonin (5-HT) receptors, are not only present in the sensory nervous system and the autonomic nervous system, but distributed in the central nervous system. As the whole aspect of the 5-HT.sub.3 receptors is being revealed, it has been suggested that the clinical application of antagonistic drugs for the receptors can range widely from the peripheries to the center.
It has been known that the compounds showing an antagonistic activity for 5-HT.sub.3 receptors are useful for the treatment of disturbances in central nervous systems such as depression, anxiety, schizophrenia and dementia, for the prophylaxis or treatment of digestive diseases such as indigestion, nausea, vomiting, diarrhea, indefinite complaint of alimentary system, irritable bowel syndrome, and/or for the relief or treatment of dependance induced by drug abuse. As such 5-HT.sub.3 receptor-blocking agent, ICS 205-930 ((3.alpha.-tropanyl)-1H-indole-3-carboxylic acid ester), Ondansetron (1,2,3,9-tetrahydro-9-methyl-3[(2-methyl-1H-imidazole-1-yl)methyl]-4H-carb azole-4-one) and the like are known. Further, U.S. Pat. No. 4,892,872 discloses 3-oxo-2H-1,4-benzoxazine-8-carboxamide compounds which shows an antagonistic activity for 5-HT.sub.3 receptors. Further, a certain class of benzamides have a dopamine D.sub.2 receptor-blocking activity and are useful as drugs for the treatment of schizophrenia or as anti-vomiting drugs. For example, Sulpiride (2-methoxy-N-(1-ethyl-2-pyrrolidinylmethyl)-5-sulfamoylbenzamide) is being used as a drug for the treatment of schizophrenia or peptic ulcer, while Metoclopramide (4-amino-5-chloro-N-(2-diethylamine)ethyl-2-methoxybenzamide) is being used as prokinetics or as anti-vomiting drugs.
As a result of studies made by the present inventors, a series of novel compounds having a different structure from those of the above-mentioned compounds and having a 5-HT.sub.3 receptor-blocking activity and/or a 5-HT.sub.1A receptor-blocking activity and/or a 5-HT.sub.2 receptor-blocking activity and/or dopamine D.sub.2 receptor-blocking activity were found.